Colorants in foods are either natural pigments or synthetic compounds. There is a need for natural red-hue colorants that can serve as an alternative to the existing red-hue colorants, such as, FD&C Red No. 40, for use as an additive to foodstuffs, beverages, pharmaceuticals, toiletries, and the like. Various colorants have been produced by extraction of various fruits and vegetables. For example, in U.S. Pat. Nos. 4,452,822 and 4,500,556, anthocyanins are extracted from grape pomace to produce a colorant. However, such colorant extracts include residual organic compound residues due to the manner of extraction and do not possess a red-hue equivalent to FD&C Red No. 40.
Red cabbage and purple carrots have also been extracted to obtain natural colorants. Both the red cabbage and purple carrot extracts, however, do not provide a red-hue colorant equivalent to the red hue of FD&C Red No. 40. Anthocyanins have also been extracted from radishes to provide a red-hue colorant. However, the radish extracts possess a relatively strong and unpleasant flavor (and odor) due to the presence of glucosinolate break-down products, making the radish colorant undesirable for foodstuffs and beverages.
There has been some (unsuccessful) research regarding the use of various potato extracts as a source for natural colorants. Some of the research has been directed to potato cultivars rich in anthocyanin pigments, but the extract is of a purple hue rather than a red hue.
Natural fruit and vegetable juices have been approved by the FDA as colorants as long as a physical separation or extraction of the colorants is performed. That is, chemical separation means cannot be used to separate the colorants, only physical separation processes, such as by dehydration, concentration, and membrane-separation technology. Aqueous fruit and vegetable extractions are also considered physical separations of the colorant. Thus, it is relatively easy and inexpensive to obtain FDA approval for such "natural colorants."
It may be possible to prepare a relatively stable, red-potato anthocyanin extract by absorption of potato extract on a C-18 silica resin. Such extractions, however, have not previously been performed because subsequent extraction with an acidic alcohol is necessary. The Food and Drug Administration (FDA) has very strict standards and requirements for approval of such a colorant extract for use as food colorants because organic solvents are used for the extraction process (i.e., a chemical separation process is used). The organic solvent extraction typically leaves residual amounts of the organic solvent in the extract. Accordingly, if such a chemical separation process is used, the FDA requires extensive and costly toxicological and safety tests be performed before such a colorant could be considered and possibly approved by the FDA. Even then, it may not be possible to sufficiently remove the organic solvent residuals from the extract such that the extract could be used as a food colorant.
Potato anthocyanins have not been used as colorants because potatoes, both cultivated and wild potatoes, contain steroidal glycoalkaloids. Specifically, steroidal glycoalkaloids ("SGAs" or "alkaloids"), a class of nitrogen containing compounds that possess the C.sub.27 skeleton of cholestane, are present in cultivated and wild potatoes. The major alkaloids in commercial potatoes are .alpha.-solanine and .alpha.-chaconine, which are glycosylated derivatives of the aglycone solanidine. Potato breeding typically introduces desired traits (e.g., frost, disease, and pest resistance) but tends to result in increased concentrations of such alkaloids. Alkaloids are natural toxins in potatoes that probably evolved as protective compounds in response to tissue invasion. Alkaloids have antimicrobial, insecticidal, and fungicidal properties that provide resistance against several insect pests and herbivores. Roddick et al., Membrane Disrupting Properties of the Steroidal Glycoalkaloids Solasonine and Solamargine, Phytochemistry, Vol. 29, pp. 1513-1518 (1990); Tingey, Clycoalkaloids as Pest Resistance Factors, Am. Potato Journal, Vol. 61, pp. 157-167 (1984); Schreiber, Steroid Alkaloids: the Solanum Group, R.H.F. Academic Press, N.Y., pp. 1-192 (1968). However, alkaloids possess pharmacological and toxicological effects that are harmful to human beings. Van Gelder, Chemistry, Toxicology and Occurrence of Steroidal Glycoalkoloids: Potential Contaminants of the Potato, Eds. Abbel-Fattah and Rizk, CRC Press, FL, pp. 117-156 (1991); Jadhav et al., Naturally Occurring Toxic Alkaloids in Food, Crit. Rev. Toxicol., Vol. 9, pp. 21-104 (1981). Alkaloids along with cyanogenic glucosinolates are responsible for more human illnesses and deaths than any other plant toxicants. Hall, Toxicological Burdens and the Shifting Burden of Toxicology, Food Technol., Vol. 46, pp. 109-112, (1992).
A safety level for acceptable alkaloid concentrations in potatoes was established at 200 mg/kg for acute toxicity, but these levels do not account for possible subacute or chronic effects. An upper limit of 60 mg/kg to 70 mg/kg has been proposed for potato cultivars selected for human consumption. Valkonen et al., Potato Glycoalkaloids: A Burden or a Blessing?, Crit. Rev. Plant Sci., Vol. 15(1), pp. 1-20, (1996); Van Gelder, Chemistry, Toxicology and Occurrence of Steroidal Glycoalkoloids: Potential Contaminants of the Potato, Eds. Abbel-Fattah and Rizk, CRC Press, FL, pp. 117-156 (1991).
The FDA requires that the concentration of alkaloids in potato cultivars be below a particular level before the potato is approved for human consumption. The FDA also requires documentation of the alkaloid concentration of newly developed cultivars. A problem in extracting anthocyanin from potatoes is that the anthocyanin extract of the potatoes also contains such alkaloids. Accordingly, potato extracts have not heretofore been developed for use as red-hue colorants.
The alkaloid concentrations in red-fleshed potato anthocyanin extracts are of concern since they tend to be concentrated along with the anthocyanin pigments. Alkaloids are fairly heat-stable compounds, slightly affected by steaming, boiling, baking, frying, cooking and microwaving of potatoes. Friedman et al., Potato Clycoalkaloids: Chemistry, Analysis, Safety, and Plant Physiology, Crit. Rev. Plant Sci., Vol. 16(1), pp.55-132, (1997); Van Gelder, Chemistry, Toxicology and Occurrence of Steroidal Glycoalkoloids: Potential Contaminants of the Potato, Eds. Abbel-Fattah amd Rizk, CRC Press, FL, pp. 117-156 (1991). Alkaloids will precipitate under basic conditions. The stability of the anthocyanins, however, is affected by basic pH. A basic pH increases the rate of degradation of the anthocyanin pigments, and hence any colorant formed by the same. Wrolstad, Colorants in Food Chemistry: Principles and Applications, Ed. Christen, G. L., AFNC Press, CA (1999); Francis, Food Colorants: Anthocyanins, Crit. Rev. Food Sci. and Nutr., Vol. 28(4), pp. 273-314 (1989); Harib et al., The Effect of Oxygen and Hydrogen Ion Concentration on Color Changes in Processed Beets, Strawberries and Raspberries, Proc. Am. Soc. Hort. Sci., Vol. 68, p. 482 (1956).
Further, potatoes contain polyphenoloxidase (PPO) which also presents a problem when extracting anthocyanin pigments from potatoes for use as colorants. That is, the extract would likely contain such PPO. PPO, polymerized phenolics, react with anthocyanin pigments, accelerating degradation of the anthocyanin colorant to produce an undesirable browning of the extract.
The present invention provides a natural, red-hue colorant compositions that are substantially free of alkaloids and PPO, has good stability, minimal aroma, minimal taste, and does not contain any organic solvent residuals. The natural colorant compositions further provide a red-hue equivalent to the red-hue of FD&C Red No. 40 and are more stable than existing red-hue natural colorants. The natural colorant compositions also provide a semi-purified alkaloid fraction. Such purified alkaloid fraction may be used as a natural pesticide, herbicide, antimicrobial agent, insecticide, or fungicide.
Further, the present invention provides methods for preparing colorant compositions comprising anthocyanin pigments extracted from red-fleshed potatoes without use of an organic solvent, while essentially eliminating alkaloids and PPO from the extract. The disclosed methods of the present invention provide production of natural colorant compositions having a red-hue equivalent to FD&C Red No. 40. Moreover, the disclosed natural colorant compositions and methods of making the same, meet FDA classification parameters as a colorant exempt from severe certification requirements (i.e., the process is a "physical separation" rather than a "chemical separation"). The disclosed method and corresponding natural colorants fall within the group of natural vegetable juices that are already approved by the FDA.
Specifically, in a method of the present invention, potato slices are pressed and filtered. The filtrate (i.e., potato juice containing potato anthocyanin pigments) is then concentrated and the pH of the concentrate is adjusted with alkali to precipitate alkaloids. Adjustment of the pH of an anthocyanin extract has not before been considered appropriate because alkali saponifies the acylated anthocyanins. Additionally, such a pH adjustment of an anthocyanin extract typically accelerates the degradation of the anthocyanin. In the present methods, however, the conditions for pH adjustment have been optimized to maximize the precipitation of unacceptable alkaloids while minimizing saponification and degradation of the anthocyanin pigments.
After the alkaloids are precipitated, the concentrate is filtered and the pH of the filtrate is adjusted to a relatively low pH value. The pH is adjusted in such a manner to obtain a colorant having the desired red-hue color and intensity (i.e., a natural colorant having a red-hue equivalent to FD&C Red No. 40). Additionally, acid adjustment of the filtrate to a relatively low pH value improves the stability of the anthocyanin pigments.
The foregoing and other features and advantages of the present invention will become more apparent from the following detailed description, drawings, and examples of the red-hue natural colorant compositions and methods for making the same.